Whether you use a 1901 or 1902 can be subjective based on your individual tastes.  I personally prefer the 1902 with the Sgt. Peep extended.  Many shooting in matches prefer the 1901.  My advice would be to research the two sights and find what would work best for your needs.  If you install the 1901, and then find you would rather have a 1902, you're going to have to purchase another hand guard and rear sight!!! 

Also, if you're going to shoot in matches (Roosevelt or Vintage), you'll need to decide if you'll use the peep or not.  The Peep on Krag sights is unbelievably small (0.04), however you can legally alter the rear sight per CMP rules to enlarge the peep up to 0.1.  The Sgt. Peep on the 1902 sight can only be enlarged to around 0.07 before you damage the plate... but that is sufficient to make the sight very useable... and accurate!!!

Finally, if you intend on shooting your Krag in matches, there will be no shortage of people here (yours truly included) to help you get started!

Paul